PROJECT SUMMARY/ABSTRACT Chlamydia infections are the most commonly reported infectious disease in the U.S. Chlamydia causes respiratory infections and genital infections, which disproportionally harm women because they can lead to infertility and ectopic pregnancy. Chlamydia is known to affect motile cilia, which are cell surface projections that play a critical role in transport of an ovum from the ovaries through the Fallopian tubes to the uterus. However, it is not known how the Chlamydia infection affects motile cilia. To study effects of Chlamydia on motile cilia, we are developing a novel, physiologically-relevant Chlamydia infection model that utilizes primary human epithelial cells. These cells differentiate into highly-ciliated cells by growth at the air-liquid interface, which mimics the natural environment of the respiratory and genital tracts. With this novel infection model, we have detected Chlamydia-induced motile cilia loss. This host pathogen interaction has not been apparent in standard Chlamydia cell culture infections, which use cells that do not have motile cilia. In Aim 1, we will first optimize this novel infection model to improve the infection efficiency. We will then use confocal microscopy, to measure the extent and time course of cilia loss in Chlamydia-infected cells, and high- speed video microscopy to quantify defects in cilia activity and number. In addition, we will test effects of different chlamydial strains on motile cilia. Our preliminary studies have used multiciliated primary epithelial cells from the trachea, but we will extend these studies to fallopian tube epithelial cells. In Aim 2, we will investigate the mechanism of Chlamydia-induced motile cilia loss. We will use confocal and electron microscopy to look for alterations to basal bodies as a sign of a cilia formation defect. To test if there is a defect in cilia disassembly, we will use CRISPR/Cas 9 and inhibitor approaches to test if the AurA-HDAC6 cilia disassembly pathway is necessary for Chlamydia-induced motile cilia loss. Successful completion of these studies will lead to a new infection model of multiciliated epithelial cells, which are present at natural sites of infection but not in conventional Chlamydia cell culture infection models. We will also define a novel mechanism in which an infectious agent causes motile cilia loss. Inhibitors that prevent Chlamydia-induced cilia loss by targeting the AurA pathway may form the basis for a novel therapeutic strategy to treat chlamydial infections and preserve fertility.